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Animal Behavior

Jan. 23, 2013 — In experiments on rats outfitted with tiny goggles, scientists say they have learned that the brain’s initial vision processing center not only relays visual stimuli, but also can “learn” time intervals and create specifically timed expectations of future rewards. The research, by a team at the Johns Hopkins University School of Medicine and the Massachusetts Institute of Technology, sheds new light on learning and memory-making, the investigators say, and could help explain why people with Alzheimer’s disease have trouble remembering recent events.

Results of the study, in the journalNeuron, suggest that connections within nerve cell networks in the vision-processing center can be strengthened by the neurochemical acetylcholine (ACh), which the brain is thought to secrete after a reward is received. Only nerve cell networks recently stimulated by a flash of light delivered through the goggles are affected by ACh, which in turn allows those nerve networks to associate the visual cue with the reward. Because brain structures are highly conserved in mammals, the findings likely have parallels in humans, they say.

“We’ve discovered that nerve cells in this part of the brain, the primary visual cortex, seem to be able to develop molecular memories, helping us understand how animals learn to predict rewarding outcomes,” says Marshall Hussain Shuler, Ph.D., assistant professor of neuroscience at the Institute for Basic Biomedical Sciences at the Johns Hopkins University School of Medicine.

To maximize survival, an animal’s brain has to remember what cues precede a positive or negative event, allowing the animal to alter its behavior to increase rewards and decrease mishaps. In the Hopkins-MIT study, the researchers sought clarity about how the brain links visual information to more complex information about time and reward.

The presiding theory, Hussain Shuler says, assumed that this connection was made in areas devoted to “high-level” processing, like the frontal cortex, which is known to be important for learning and memory. The primary visual cortex seemed to simply receive information from the eyes and “re-piece” the visual world together before presenting it to decision-making parts of the brain.

To monitor the vision-reward connection process, the team fitted rats with special goggles that let researchers flash a light before either their left or right eye. Thirsty rats with goggles were given access to a water spout inside a testing chamber. When they approached the water spout, a brief visual cue was presented to one eye.

If light was sent to the left eye, the water spout would have to be licked a few times before water came to the rat; if light was sent to the right eye, the rat would have to lick many more times before water came. After a few daily sessions of such “conditioning” (not unlike Pavlov’s famous dog-bell-reward experiments), the rats learned how long they would have to lick before getting a water reward. If they didn’t get the reward in the expected amount of time, they would give up and leave the spout.

Monitoring the pattern of electrical signals given off by individual nerve cells in the rat brains, the researchers found that the signals’ “spikes” weren’t just reflecting the visual cue alone. Rather, the signals seemed to relay the time of expected reward delivery through altered spiking patterns. They also saw that many nerve cells seemed to report one or the other visual cue-reward interval, but not both. In cells stimulated by a flash to the left eye, the electrical signal returned to its baseline after a short delay, in sync with the timing of the water reward; a cue to the right eye correlated with a longer delay, also in sync with the reward. According to the researchers, the amount of time that passed before nerve cells returned to their resting state was the brain’s way of setting up a “timed expectation.”

Knowing that the basal forebrain is implicated in learning, the researchers wanted to know if their observations could be explained by nerves from the basal forebrain delivering ACh to the vision-processing center. To remove those nerve cells from the equation, they paired a neurotoxin with a “homing device” that targets only ACh-releasing neurons coming from the basal forebrain. They then repeated their experiments in trained rats that received the neurotoxin and in those that didn’t, and found that the nerve cell signals continued to relay the old time intervals, suggesting that ACh and the basal forebrain weren’t needed to express previously learned time information.

The researchers next used those same rats to ask if ACh is necessary for nerve cells to learn new time delays. To do that, they switched the visual cues so that a flash in the left eye meant a long delay and one in the right eye meant a short one. Vision-processing nerve cells in the rats in which ACh delivery was left intact adapted their signals to the new associations; but those in the rats that no longer received ACh continued to relay the old associations, suggesting that ACh is necessary to make new associations but not to express old ones.

Hussain Shuler explains, “When a reward is received, ACh is sent throughout the brain and reinforces only those nerve cell connections that were recently active. The process of conditioning continues to strengthen these nerve connections, giving rise to a timed expectation of reward in the brain.”

According to Hussain Shuler, studies have shown that Alzheimer’s patients have low levels of ACh and have trouble forming new memories. Though medication may elevate ACh, alleviation of symptoms is limited. “Our research explains that limitation,” he says. “Therapeutically, we predict that the problem isn’t just low levels of ACh — the timing of ACh delivery is key.”

Other authors of the report include Emma Roach of the Johns Hopkins University School of Medicine and Alexander Chubykin and Mark Bear of the Massachusetts Institute of Technology.

This work was supported by grants from the National Institute of Mental Health (R01MH084911), the National Institute on Drug Abuse (F31DA026687), the National Eye Institute (R01EYO12309), the National Institute of Child Health and Human Development (R01HD046943) and The Johns Hopkins University.

Jan. 23, 2013 — All parents know the infant milestones: turning over, learning to crawl, standing, and taking that first unassisted step. Achieving each accomplishment presumably requires the formation of new connections among subsets of the billions of nerve cells in the infant’s brain. But how, when and where those connections form has been a mystery.

A mouse pup learns to use its whiskers to sense objects at about the second week of life. The nerve connections that enable this activity are helping researchers at Duke Medicine learn how human brains develop and function. (Credit: Image courtesy of Duke University Medical Center)

Now researchers at Duke Medicine have begun to find answers. In a study reported Jan. 23, 2013, in the scientific journal Neuron, the research team describes the entire network of brain cells that are connected to specific motor neurons controlling whisker muscles in newborn mice.

A better understanding of such motor control circuits could help inform how human brains develop, potentially leading to new ways of restoring movement in people who suffer paralysis from brain injuries, or to the development of better prosthetics for limb replacement.

“Whiskers to mice are like fingers to humans, in that both are moving touch sensors,” said lead investigator Fan Wang, PhD, associate professor of cell biology and member of the Duke Institute for Brain Sciences. “Understanding how the mouse’s brain controls whisker movements may tell us about neural control of finger movements in people.”

Mice are active at night, so they rely heavily on whiskers to detect and discriminate objects in the dark, brushing their whiskers against objects in a rhythmic back-and-forth sweeping pattern referred to as “whisking.” But this whisking behavior does not appear until about two weeks after birth, when young mice start to explore the world outside their nest.

To learn how motor control of whiskers takes place, Wang and postdoctoral fellow Jun Takatoh used a new technique that takes advantage of the rabies virus’ ability to spread through connected nerve cells. A disabled form of the virus used to vaccinate pets was created with the ability to express a fluorescent protein. The researchers were able to trace its path through a network of brain cells directly connected to the motor neurons controlling whisker movement.

“The precision of this mapping method allowed us to ask a key question, namely are parts of the whisker motor control circuitry not yet connected in newborn mice, and are such missing links added later to enable whisking?” Wang said.

By taking a series of pictures in the fluorescently labeled brains during the first two weeks after birth, the research team chronicled the developing circuits before and after mice start whisking.

“When we traced the circuit it was stunning in the sense that we didn’t realize there are so many pools of neurons located throughout the brainstem that are connected to whisker motor neurons,” said Wang. “It’s remarkable that a single motor neuron receives so many inputs, and somehow is able to integrate them.”

At the same time whisking movements emerge, motor neurons receive a new set of inputs from a region of the brainstem called the LPGi. A single LPGi neuron is connected to motor neurons on both sides of the face, putting them in perfect position to synchronize the movements of left and right whiskers.

To learn more about the new circuit formed between LPGi and motor neurons, Wang and Takatoh drew on the expertise of Duke colleague Richard Mooney, PhD, professor of neurobiology, and his student Anders Nelson. Together, the researchers were able to record the labeled neurons and found the LPGi neurons communicate with motor neurons using glutamate, the main neurotransmitter that stimulates the brain. They further discovered that LPGi neurons receive direct inputs from the motor cortex.

“This makes sense because exploratory whisking is a voluntary movement under control of the motor cortex,” Wang said. “Excitatory input is needed for initiating such movements, and LPGi may be critical for relaying signals from the motor cortex to whisker motor neurons.”

The researchers will next explore the connectivity by using genetic, viral and optical tools to see what happens when certain components of the circuits are activated or silenced during various motor tasks.

In addition to Wang, Takatoh, Mooney and Nelson at Duke, study authors include Xiang Zhou of the University of Chicago; Michael D. Ehlers of Pfizer Inc. R&D; M. McLean Bolton of the Max Planck Institute; and Benjamin R. Arenkiel of Baylor College of Medicine.

The research was supported by grants from the National Institutes of Health (DA028302, DE19440, NS079929) and by the Duke Institute for Brain Sciences.

Jan. 21, 2013 — Endangered Mexican howler monkeys are consuming more leaves and less fruit as a result of habitat disturbance by humans, which is forcing them to invest much more time foraging for sustenance and leading to increased ‘stress’ levels, as detected through hormone analysis.

The research, published January 22 in the International Journal of Primatology, took place in the tropical rainforests of the Mexican state of Veracruz, which are being deforested and fragmented by human activity — primarily the clearing of forest for cattle raising. It shows that increases in howler monkey ‘travel time’ — the amount of time needed to find requisite nourishment — are leading to increases in levels of stress hormones called glucocorticoids.

These hormones are not only indicators of stress, but are also known to relate to diminished reproductive success and lower survival rates. Researchers believe the study could serve as a model for behavioural change and resulting health implications more generally in primates living in habitats disturbed by human activities, such as deforestation.

“Howlers are arboreal primates, that is to say they spend their wholes lives in the trees,” said Dr Jacob Dunn from Cambridge’s Department of Biological Anthropology, who carried out the research.

“As forests are fragmented, the howlers become cut off, isolated on forest ‘islands’ that increasingly lack the fruit which provide an important component of their natural diet. This has led to the monkeys expending ever more time and effort foraging for food, often increasing leaf consumption when their search is, quite literally, fruitless.”

Fruit occurs in natural cycles, and the monkeys will naturally revert to ‘fallback’ foods, including leaves, when fruit is scarce. But as habitats shrink, and fruit is harder to find, leaves from second-choice plants, such as lianas, have increased in the Mexican howlers’ diet.

While leaves may sound like a plentiful resource in a rainforest, many leaves are difficult to digest and can be filled with toxins — a natural defence mechanism in most trees and plants — so the monkeys are actually forced to spend more time seeking out the right foliage to eat, such as new shoots which are generally less toxic.

“The traditional view was that the leaves exploited by howler monkeys were an abundant food source — but this is not the case,” said Dunn.

“The monkeys rely much more heavily on fruit than previously believed, and when turning to foliage for food — as they are increasingly forced to do — they have to be highly selective in the leaves they consume, visiting lots of different trees. This leads to the increased ‘travel time’ and consequent high levels of stress we are seeing in these primates as their habitats disintegrate.”

As trying to catch the howlers to examine them would in itself be highly stressful for the animal, the best way of evaluating stress levels in wild primates is by analysing their faeces for glucocorticoid stress hormones, which are general to all vertebrates.

Through statistical modelling, the researchers were able to determine that it is the ‘travel time’ — rather than the increased foliage intake — causing high levels of stress.

“Monkeys in disturbed habitats suffering high levels of stress is in itself unsurprising perhaps, but now we think we know why, the root cause from the primates perspective. Our results also highlight the importance of preserving and planting fruit trees — particularly those species such as figs that can produce fruit during periods of general fruit scarcity — for the conservation of howler monkeys¨ said Dr Jurgi Cristóbal-Azkarate, also from Cambridge, who led the research in collaboration with Dr Joaquim Vea from the University of Barcelona.

The authors say that further studies are required to fully understand the significance of increases in stress in howler monkeys living in disturbed habitats. “Determining the full relevance of our results for the conservation of primates living in forest fragments will require long-term studies of stress hormones and survival,” said Dunn.

Jan. 17, 2013 — Is athleticism linked to brain size? To find out, researchers at the University of California, Riverside performed laboratory experiments on house mice and found that mice that have been bred for dozens of generations to be more exercise-loving have larger midbrains than those that have not been selectively bred this way.

This image shows a 3-D reconstruction of a mouse brain based on magnetic resonance imaging (MRI). The forebrain is seen in green, the midbrain in yellow and the cerebellum in orange. The forebrain region has been made partially transparent to show the underlying regions (from left to right, the hippocampus and caudate). (Credit: Garland Lab, UC Riverside)

Theodore Garland’s lab measured the brain mass of these uniquely athletic house mice, bred for high voluntary wheel-running, and analyzed their high-resolution brain images. The researchers found that the volume of the midbrain — a small region of the brain that relays information for the visual, auditory, and motor systems — in the bred-for-athleticism mice was nearly 13 percent larger than the midbrain volume in the control or “regular” mice.

“To our knowledge, this is the first example in which selection for a particular mammalian behavior — high voluntary wheel running in house mice in our set of experiments — has been shown to result in a change in size of a specific brain region,” said Garland, a professor of biology and the principal investigator of the research project.

Study results appeared online Jan. 16 in The Journal of Experimental Biology.

In Garland’s lab, selection for high voluntary wheel running in lab house mice has been ongoing for nearly 20 years — or more than 65 generations of house mice. To analyze brain mass and volume on independent samples of house mice, the researchers dissected the brains into two different regions, the cerebellum, a region of the brain crucial for controlling movement, and the non-cerebellar areas. They then weighed these sections separately.

The cerebellum is important for coordination. The midbrain, a part of the non-cerebellar area that contains a variety of sensory and motor nuclei, is essential for reward learning, motivation and reinforcing behavior. Previously, species of mammals and birds with larger brains have been shown to have higher survivability in novel environments.

The researchers found that compared to regular mice, those mice that had been selectively bred for high voluntary wheel-running had significantly greater midbrain volume as well as larger non-cerebellar brain mass, but not larger cerebella or total brain mass.

The primary question the researchers sought to answer in their study is whether selection on a particular behavioral trait, such as voluntary exercise, using an experimental evolution paradigm, has resulted in a change in brain size. An additional question they posed is whether any change in brain size involves the entire brain or is “mosaic,” that is, involving only a section or some sections of the brain.

“Our finding that mice bred for high levels of voluntary exercise have an enlarged non-cerebellar brain mass and an enlarged midbrain, but do not show a statistically significant increase in overall brain mass or volume supports the mosaic theory of brain evolution,” Garland said.

What implications the current research has for humans is not immediately clear.

“It is possible that individual differences in the propensity or ability for exercise in humans are associated with individual differences in the size of the midbrain, but no one has studied that,” Garland said. “If it were possible to take MRIs of babies’ midbrains before these babies started ‘exercising’ and then follow these babies through life, it may be that inherent, genetically-based differences in midbrain size detected soon after birth will influence how much they would be likely to exercise as adults.”

Jan. 17, 2013 — New research led by a team at Queen Mary, University of London, has found evidence of how daily changes in temperature affect the fruit fly’s internal clock.

“A wide range of organisms, including insects and humans, have evolved an internal clock to regulate daily patterns of behaviour, such as sleep, appetite, and attention,” explains Professor Ralf Stanewsky, senior study author from Queen Mary’s School of Biological and Chemical Sciences.

“Research on animal and human clocks shows that they are fine tuned by natural and human-made time cues, for example the daily changes of light and temperature, alarm clocks and ‘noise-pollution’. Understanding the principles of clock synchronisation could be useful in developing treatments against the negative effects of sleep-disorders and shift-work. This research has many implications because it extends our knowledge of how the environment influences body clocks.”

Scientists have a good understanding of how light affects the internal body clock, also known as the circadian clock. Specially evolved cells in the brain contain the circadian clock, which needs to be synchronised with the natural environment every day to help them run on time.

In this new study, the researchers made groups of fruit flies ‘jet-lagged’ by exposing them to daily temperature changes reflecting warmer or colder climates to understand how temperature affects the circadian clock.

The team discovered that a group of ‘dorsal clock cells’ found in the back of the fly’s brain was more important for clock-synchronisation at warmer temperatures. But a group of ventral clock cells found further to the front of the brain played an important role at the cooler temperature range. In addition to their clock function, these cells also act like a thermometer, being more active at certain temperatures.

The research also shows that removing the light-receptor Cryptochrome, an important component in synchronising the clock to the daily light changes, leads to the flies being more sensitive to temperature changes. This could help to explain why daily light changes, which are a more reliable time cue compared to the daily temperature fluctuations, are the dominant signal in nature for synchronising the clock.

Jan. 10, 2013 — Animals are more eloquent than previously assumed. Even the monosyllabic call of the banded mongoose is structured and thus comparable with the vowel and consonant system of human speech. Behavioral biologists from the University of Zurich have thus become the first to demonstrate that animals communicate with even smaller sound units than syllables.

(Credit: Image courtesy of University of Zurich)

When humans speak, they structure individual syllables with the aid of vowels and consonants. Due to their anatomy, animals can only produce a limited number of distinguishable sounds and calls. Complex animal sound expressions such as whale and bird songs are formed because smaller sound units — so-called “syllables” or “phonocodes” — are repeatedly combined into new arrangements. However, it was previously assumed that monosyllabic sound expressions such as contact or alarm calls do not have any combinational structures. Behavioral biologist Marta Manser and her doctoral student David Jansen from the University of Zurich have now proved that the monosyllabic calls of banded mongooses are structured and contain different information. They thus demonstrate for the first time that animals also have a sound expression structure that bears a certain similarity to the vowel and consonant system of human speech.

Single syllable provides information on the identity and activity of the caller

The research was conducted on wild banded mongooses at a research station in Uganda. For their study, the scientists used a combination of detailed behavior observations, recordings of calls and acoustic analyses of contact calls. Such a call lasts for between 50 and 150 milliseconds and can be construed as a single ‘syllable’. Jansen and his colleagues now reveal that, despite their brevity, the monosyllabic calls of banded mongooses exhibit several temporally segregated vocal signatures. They suspected that these were important so studied the individual calls for evidence of individuality and behavior. “The initial sound of the call provides information on the identity of the animal calling,” explains Jansen. The second more tonal part of the call, which is similar to a vowel, however, indicates the caller’s current activity.

Structured single syllables in animals not an exception?

Manser and her team are thus the first to demonstrate that animals also structure single syllables — much like vowels and consonants in human speech. The researchers are convinced that the banded mongoose is not the only animal species that is able to structure syllables. They assume that the phenomenon was overlooked in scientific studies thus far. For instance, they point out that frogs and bats also structure single syllables. “The example of banded mongooses shows that so-called simple animal sound expressions might be far more complex than was previously thought possible.”

About Banded mongooses

Banded mongooses (Mungo mungos) live in the savannah regions south of the Sahara. They are small predators that live in social communities and are related to the meerkat (Suricata suricatta). Banded mongooses differ from meerkats and other mammals that rear their young cooperatively in that several females have offspring. In the case of meerkats, however, only the dominant female has young.

Banded mongoose groups each comprise around twenty adult animals. The group looks after the young animals, defends its territory jointly and forages as a unit. As soon as the young go foraging with the group, they enter into an exclusive, one-on-one relationship with an adult animal, an escort. The young recognize their escort based on its call and are able to distinguish it from other group members. Banded mongooses have a wide range of sounds and coordinate their activities by this means, which enables them to maintain group cohesion.

Jan. 8, 2013 — In mam mals such as rodents that raise their young as a group, infants will nurse from their mother as well as other females, a dynamic known as allo suck ling. Ecol o gists have long hypoth e sized that allo suck ling lets new borns stock pile anti bod ies to var i­ous dis eases, but the exper i­men tal proof has been lack­ing until now.

An in-press report in the jour nalMam malian Biol ogy found that infant Mon go lian ger bils that suck led from females given sep a rate vac cines for two dif fer ent dis eases wound up with anti bod ies for both illnesses.

The find ings not only demon strate the poten tial pur pose of allo suck­ling, but also pro vide the first frame­work for fur ther study ing it in the wild by using trace able anti bod ies, said first author Romain Gar nier, a post­doc toral researcher in Prince ton University’s Depart ment of Ecol ogy and Evo lu tion ary Biol ogy. Gar nier con ducted the research with Syl vain Gan don and Thierry Boulin ier of the Cen ter for Func tional and Evo lu tion­ary Ecol ogy in France, and with Yan nick Chaval and Nathalie Char­bon nel at the Cen ter for Biol ogy and Man age ment of Pop u la tions in France.

Gar nier and his coau thors admin is­tered an influenza vac cine to one group of female ger bils, and a vac­cine for Bor re lia burgdor feri — the bac te r ial agent of Lyme dis ease — to another group. Once impreg nated, female ger bils from each vac cine group were paired and, as the ger­bils do in nature, kept sep a rate from the male ger bils to birth and rear their young. In the wild, females can choose which young to nurse and infant ger bils can like wise choose which female to suckle. In the typ i cal lab, how ever, one male, one female and their young are housed together, the researchers wrote.

When screened upon birth, all the infant ger bils had no detectable anti bod ies against influenza while one had anti­bod ies against B. burgdor feri, accord ing to the paper. But after eight days of nurs ing, all the infants con tained high lev els of anti bod ies for both influenza and B. burgdor feri, sug gest ing that the females nursed the young — their own and those of the other female — evenly. These results sug gest that allo­suck ling is indeed intended to expose new born ani mals to a host of antibodies.

This ben e fit sheds light on a pecu liar arrange ment in coop er a­tive mam mals that ecol o gists have puz zled over, the authors wrote. In social species, females usu ally fall into dom i nant or sub or di nate groups with the sub or di nate females typ i cally involved in tend ing to the young pro duced by dom i nant females. Yet, in many cases, sub or di nate females are “allowed” to breed. Gar nier and his col leagues sug gest that the poten tially larger anti body pool avail able through nurs ing might be one of the rea sons why.

Jan. 9, 2013 — Two years of painstaking observation on the social interactions of a troop of free-ranging monkeys and an analysis of their family trees has found signs of natural selection affecting the behavior of the descendants.

A family of rhesus macaques. (Credit: Image courtesy of Duke University)

Rhesus macaques who had large, strong networks tended to be descendants of similarly social macaques, according to a Duke University team of researchers. And their ability to recognize relationships and play nice with others also won them more reproductive success.

“If you are a more social monkey, then you’re going to have greater reproductive success, meaning your babies are more likely to survive their first year,” said post-doctoral research fellow Lauren Brent, who led the study. “Natural selection appears to be favoring pro-social behavior.”

The analysis, which appears January 9 in Nature’s Scientific Reports, combined sophisticated social network maps with 75 years of pedigree data and some genetic analysis.

The monkeys are a free-ranging population of macaques descended from a 1938 release of monkeys from India on undeveloped 38-acre Cayo Santiago Island, off the eastern coast of Puerto Rico. They live in a natural setting with little human intervention other than food provisioning, but they do have university students watching them a lot of the time.

Field researchers who had learned to identify each of the nearly 90 monkeys on sight carefully logged interactions between individuals in 10-minute episodes over a two-year span. They compiled four or five hours of data per individual, logging grooming, proximity and aggression.

From that, the team built web-like network maps to analyze pro-social and anti-social interactions. They also looked at the maps for a measure they called “betweenness” — the shortest paths between individuals — and “eigenvector,” a friends-of-friends measure that shows how many friends each friend of an individual has.

“The really ‘popular’ monkeys would have a high eigenvector, or a really big friends-of-friends network,” Brent said. There were also less-popular outliers who had fewer social interactions and a lower eigenvector. “They’re sort of the dorks,” Brent said.

When these measures were then compared to family trees, “a lot of these network measures popped out as having significant heritability,” Brent said. That is, the behaviors seemed to run in families.

“This is really a landmark paper,” said James Fowler, a professor of medical genetics and political science at the University of California-San Diego who studies human social networks, including Facebook, but who was not part of the study. “They’re showing that the positive behaviors which build social networks might be heritable, and that’s consistent with what we’ve been seeing in human studies.”

The analysis of aggression didn’t reveal much heritability, but it did influence reproductive success. At either end of the aggression scale, monkeys who were the most aggressive and those who were the most passive had better reproductive success than the monkeys in the middle.

The team also collected blood samples and did some genetic analysis on two genes in the serotonin system of the monkeys. Variability in the two genes — one that makes serotonin and one that carries it around — was most closely associated with differences in grooming connections between the monkeys.

They chose to focus their genetic analysis on two genes in the serotonin system because there is a lot of literature on that area in humans. Serotonin, a molecule that carries signals between nerve cells, is part of the system acted on by antidepressant drugs, so it has been widely studied.

“The way that genes can affect behavior is by their influence on neural circuits,” said Michael Platt, director of the Duke Institute for a Brain Sciences and the Center for Cognitive Neuroscience. “We know that neural circuits for a variety of things like social behavior, food and mood are under the influence of serotonin signaling, in both humans and monkeys.”

Genes by themselves don’t determine your social standing, Platt added. But social success comes from some combination of social skills and temperament, which appear to have a genetic basis.

“We can see that some of these behaviors have a genetic basis, from what we know of the pedigrees and the network map,” Brent said. “But we’ve only scratched the surface of figuring out which specific genes are associated with each behavior.”

Fowler said the article is especially interesting coming on the heels of a study in Nature last year that showed hunter-gatherer networks are not very different from those in modernized human societies. “So now the conversation is about where to draw the line — how far back did our networks evolve?” Fowler asked. “This paper suggests it may have been a common ancestor with macaques.”

Platt’s group recently won an additional five years of funding from the National Institute of Mental Health to continue and expand the study. Social network observations are now being done on other troops of monkeys on the island and the blood that has been collected will be subjected to further genetic testing.

Having 75 years of family history, combined with the latest genetic tools and a lot of observational data, is going to open up all sorts of new questions, Platt said. “This is just the first two genes,” he said. “We’ll hopefully be moving on to sequence the entire genome of each animal” to find even more associations.

“This is the first major part of what will hopefully be a very big puzzle,” Brent said.

Jan. 3, 2013 — Bigger brains can make animals, well, brainier, but that boost in brain size and ability comes at a price. That’s according to new evidence reported on January 3rd inCurrent Biology, a Cell Press publication, in which researchers artificially selected guppies for large and small brain sizes.

The findings lend support to the notion that bigger brains and increased cognitive ability do go together, a topic that has been a matter of considerable debate in recent years, said Niclas Kolm of Uppsala University in Sweden. They also represent some of the first convincing evidence that large brains are expensive, evolutionarily speaking.

“We provide the first experimental evidence that evolving a larger brain really is costly in terms of both gut investment and, more importantly, reproductive output,” Kolm said.

Together, the findings strongly support the idea that relative brain sizes among species are shaped through a balance between selection for increased cognitive ability and the costs of a big brain.

The results in guppies have important implications for us humans. After all, one of the most distinctive features of the human brain is its large size relative to the rest of the body.

“The human brain only makes up 2 percent of our total body mass but stands for 20 percent of our total energy demand,” Kolm said. “It is a remarkably costly organ energetically.”

But support for the so-called “expensive-tissue hypothesis” — that there is a trade-off between the brain and the energy demands of other organs and reproduction — came only from comparative studies among species and were correlative in nature.

In the new study, Kolm’s team took a different, within-species approach. They selected live-bearing guppies for large and small brains relative to the size of their bodies. Under that strong selection pressure, they found that brain size could evolve “remarkably quickly.”

After selection, large-brained guppies outscored their smaller-brained peers in a test of numerical learning. With more energy devoted to brain-building, brainy fish — males especially — did have smaller guts. They also left fewer offspring to the next generation.

Those effects were observed despite the fact that the fish were supplied with an abundance of food. The researchers say they are curious to see what will happen in future experiments with fish in a more competitive, semi-natural environment including limited resources and predators.

The findings lead Kolm and his colleagues to suggest that the relatively small family sizes of humans and other primates, not to mention dolphins and whales, might have helped to make our big brains possible.

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ScienceDaily (Aug. 15, 2012) — A previously unrecognized system that drains waste from the brain at a rapid clip has been discovered by neuroscientists at the University of Rochester Medical Center. The findings were published online August 15 in Science Translational Medicine.

An artery in the brain of a mouse. The green shows cerebrospinal fluid in a channel along the outside of the artery. (Credit: Image courtesy of University of Rochester Medical Center)

The highly organized system acts like a series of pipes that piggyback on the brain’s blood vessels, sort of a shadow plumbing system that seems to serve much the same function in the brain as the lymph system does in the rest of the body — to drain away waste products.

“Waste clearance is of central importance to every organ, and there have been long-standing questions about how the brain gets rid of its waste,” said Maiken Nedergaard, M.D., D.M.Sc., senior author of the paper and co-director of the University’s Center for Translational Neuromedicine. “This work shows that the brain is cleansing itself in a more organized way and on a much larger scale than has been realized previously.

“We’re hopeful that these findings have implications for many conditions that involve the brain, such as traumatic brain injury, Alzheimer’s disease, stroke, and Parkinson’s disease,” she added.

Nedergaard’s team has dubbed the new system “the glymphatic system,” since it acts much like the lymphatic system but is managed by brain cells known as glial cells. The team made the findings in mice, whose brains are remarkably similar to the human brain.

Scientists have known that cerebrospinal fluid or CSF plays an important role cleansing brain tissue, carrying away waste products and carrying nutrients to brain tissue through a process known as diffusion. The newly discovered system circulates CSF to every corner of the brain much more efficiently, through what scientists call bulk flow or convection.

“It’s as if the brain has two garbage haulers — a slow one that we’ve known about, and a fast one that we’ve just met,” said Nedergaard. “Given the high rate of metabolism in the brain, and its exquisite sensitivity, it’s not surprising that its mechanisms to rid itself of waste are more specialized and extensive than previously realized.”

While the previously discovered system works more like a trickle, percolating CSF through brain tissue, the new system is under pressure, pushing large volumes of CSF through the brain each day to carry waste away more forcefully.

The glymphatic system is like a layer of piping that surrounds the brain’s existing blood vessels. The team found that glial cells called astrocytes use projections known as “end feet” to form a network of conduits around the outsides of arteries and veins inside the brain — similar to the way a canopy of tree branches along a well-wooded street might create a sort of channel above the roadway.

Those end feet are filled with structures known as water channels or aquaporins, which move CSF through the brain. The team found that CSF is pumped into the brain along the channels that surround arteries, then washes through brain tissue before collecting in channels around veins and draining from the brain.

How has this system eluded the notice of scientists up to now?

The scientists say the system operates only when it’s intact and operating in the living brain, making it very difficult to study for earlier scientists who could not directly visualize CSF flow in a live animal, and often had to study sections of brain tissue that had already died. To study the living, whole brain, the team used a technology known as two-photon microscopy, which allows scientists to look at the flow of blood, CSF and other substances in the brain of a living animal.

While a few scientists two or three decades ago hypothesized that CSF flow in the brain is more extensive than has been realized, they were unable to prove it because the technology to look at the system in a living animal did not exist at that time.

“It’s a hydraulic system,” said Nedergaard. “Once you open it, you break the connections, and it cannot be studied. We are lucky enough to have technology now that allows us to study the system intact, to see it in operation.”

First author Jeffrey Iliff, Ph.D., a research assistant professor in the Nedergaard lab, took an in-depth look at amyloid beta, the protein that accumulates in the brain of patients with Alzheimer’s disease. He found that more than half the amyloid removed from the brain of a mouse under normal conditions is removed via the glymphatic system.

“Understanding how the brain copes with waste is critical. In every organ, waste clearance is as basic an issue as how nutrients are delivered. In the brain, it’s an especially interesting subject, because in essentially all neurodegenerative diseases, including Alzheimer’s disease, protein waste accumulates and eventually suffocates and kills the neuronal network of the brain,” said Iliff.

“If the glymphatic system fails to cleanse the brain as it is meant to, either as a consequence of normal aging, or in response to brain injury, waste may begin to accumulate in the brain. This may be what is happening with amyloid deposits in Alzheimer’s disease,” said Iliff. “Perhaps increasing the activity of the glymphatic system might help prevent amyloid deposition from building up or could offer a new way to clean out buildups of the material in established Alzheimer’s disease,” he added.

In addition to Iliff and Nedergaard, other authors from Rochester include Minghuan Wang, Yonghong Liao, Benjamin Plogg, Weiguo Peng, Edward Vates, Rashid Deane, and Steven Goldman. Also contributing were Erlend Nagelhus and Georg Gundersen of the University of Oslo, and Helene Benveniste of the Health Science Center at Stony Brook University.

The work was funded by the National Institutes of Health (grant numbers R01NS078304 and R01NS078167), the U.S. Department of Defense, and the Harold and Leila Y. Mathers Charitable Foundation.